There's a pattern here, of sorts. Tony Blair became bored and frustrated with domestic policy and – heartened by success in Sierra Leone – decided that it was much more exciting to apply himself to exporting liberal democracy around the world. Hideous, inexorable foreign "adventures" followed, of course.

Gordon Brown also struggled with the detail of home affairs, most notably in his desperate, off-the-cuff pledge of "British jobs for British workers". Only when the global financial crisis struck did Brown step on to the international stage and become sure of himself (even if he didn't convince the electorate). Brown went so far, in what was surely a Freudian slip, as to declare that he had "saved the world". He hadn't. He'd just saved the Anglo-American banks.

David Cameron, too, seems to find the minutiae of domestic social policy tiresome and intractable. He stopped saying "big society" even more quickly than Blair stopped saying "Social Exclusion Unit". Cameron has already enthusiastically embraced war at the first available opportunity, against Libya. But it was his empty decision to storm out of an EU meeting seeking treaty changes to tackle the eurozone crisis that reaped the reward of a bounce in the polls. Flushed with his success as a hollow Europhobe, he has now decided that "defending Britain" is good for Conservative electability, and has started huffing and puffing about Scotland, "the union" and Holyrood's lack of constitutional power to hold a referendum anyway.

Never mind that the two impulses are at odds with each other – Cameron rejecting, even mocking, the idea of a constellation of nations being stronger in one case, and insisting that a constellation of nations is more resilient in the other. None of this is about logic. Instead it's about prime ministers finding the detail of domestic policy too difficult and complex to be reduced to simple political message, and deciding that the more monolithic concepts of nationhood or democracy are easier to abstract into the simple yes/no rhetoric of: "Are you for us, or against us?"

Of course, the perceived simplicity is deceptive. Just as the wars in Afghanistan and Iraq didn't end with flowers strewn in the paths of the liberating heroes of the west, and just as the Arab spring didn't warm into a balmy summer, Cameron's games in Europe and in the union are not as easy to control and exploit as his short-term, populist mind perceives them to be.

Still, the immediate advantages of goading Scotland are manifest. Sheer sleight-of-hand distraction from the cuts is not the least of them. Also, post-Thatcher, the Conservatives are done in Scotland. But Labour is shackled to the pro-unionist cause as well. This week, Ed Miliband stood at the dispatch box in far-off, out-of-touch Westminster and parroted the same sentiments at Scotland as the Conservatives did. Even in a country that is not yet sure that it wants full independence, that sort of thing does not go down very well at all.

One suspects that, come the next election, Cameron might prefer SNP MPs in Westminster to Scottish Labour MPs – there are already six, and a forced referendum, engineered from Westminster, supported by Labour, and delivering a No would surely, under the principle of divide and rule so recently cited by Diane Abbott, gain the SNP some more. This might not be better for democracy, for the cause of Union, for the passing of government legislation, or for resolution of the "West Lothian question" (ie the ability of Scottish MPs to vote on legislation that is devolved for Scotland and does not pertain in their own constituencies). But it sure would be better for the Conservatives' "parliamentary arithmetic", which will be so tight, after the continuing Lib-Dem immolation, that every not-Labour seat north of the border will count.

However "passionate" David Cameron feels about the union, his sudden interest in forcing a specifically yes/no Scottish independence referendum before the next election (without the devo-max option the SNP wants) is surely driven by self-interest. But that might be more dangerous than he thinks.

It's not without the bounds of logic that a No vote could actually strengthen the SNP a lot more than Cameron envisages. If Westminster does block the "devo-max" option that the Scottish electorate shows every sign of preferring, and under which Scotland would be self-governing except in foreign and defence affairs, Alex Salmond is capable of galvanising disgruntlement in Scotland over that matter, and promising to secure devo-max for Scotland the hard way.

Salmond's party might be able to persuade the Scots that the more Westminster seats the SNP gain, then the more the party could thwart the die-hard unionists, by showing them how the present system allows Scotland to hold the balance of power in England, even as it goes its own way on so many of the matters it has a vote on. That could create a stalemate, a living death for Westminster, worse by far than capitulating to devo-max. After a taste of English-democracy paralysis, the Westminster parties would be begging for the mercy that a complete and formal devo-max would deliver despite the profound changes it would necessitate at Westminster and at Holyrood.

Perhaps Salmond does secretly want, to use Cameron's excruciating pun, a neverendum, not a referendum. An endlessly deferred dream of independence doesn't stop Scotland from having something the UK does not currently have – a credible alternative to Labour and the Conservatives, headed by a credible leader who can win elections and run his government smoothly.

It's quite wrong to believe the Scottish National party would be destroyed by a rejection of independence at a referendum. As Salmond shrewdly emphasises, Scotland has every right to keep its options open, and opt for independence at a time of its own choosing. No to independence in 2014 would not be no to independence for ever, especially if the devo-max option had been stopped by the Westminster parties.

The SNP has all the time in the world, despite Cameron's insistence on the need for speed, and a great deal of resilience. Even the Conservatives, if Salmond can muster a significant number of Westminster seats, could come to realise that devo-max is in fact as good as it will get as far as preserving some form of union is concerned. Cameron thinks he's being clever by forcing Salmond's hand. He isn't. Unlike the recent succession of British prime ministers, Salmond never wavers from putting the domestic agenda first and foremost. The fact that Salmond can do this, while British prime ministers find such a focus so wearying, is in itself a lesson in why devolved government, with Westminster concentrating on the international matters that its PMs always seem to want to concentrate on anyway, would be good for Scotland, Wales, the English regions, and for all of Britain.